1. Field of the Invention
The present invention relates, in general, to a photoresist film for deep ultra violet (UV) and, more particularly, the use of a matrix resin of graft copolymer which has a desired combination of high transmittance of the backbone to deep UV with the etching resistance of the grafting moiety. Also, the present invention concerns a method for forming a photoresist film pattern by use of the photoresist film.
2. Description of the Prior Art
Usually, in order to form a pattern in a semiconductor device, a photoresist film is, first, coated on a layer to be etched and, then, patterned by exposing and developing processes. The resulting photoresist film pattern serves as a mask in etching the underlying layer.
As the integration degree of semiconductor devices becomes higher, finer photoresist film patterns are required. To satisfy this condition, chemical amplification resist films have been developed, which are found to be superior in resolution. However, the chemical amplification resist films have, in fact, not played a sufficient role in the fine pattern process using deep UV because they lack sufficiently high resolution, sensitivity, etch resistance, thermal stability, post exposure delay stability and process latitude.
A typical photoresist film comprises a matrix resin, a photo acid generator, and other additives. The matrix resin is required to be soluble to the solvent in use and show high thermal stability and low absorbance to the exposure wavelength in use in addition to having excellent etch resistance. In particular, this property is most important to photoresist film.
Matrix resins containing aromatic compounds show high etch resistance, but also high absorbance to ArF (193 nm) . In contrast, non-aromatic matrix resins have a high absorbance property to ArF (193 nm), but show poor etch resistance. These contrasting weak points are one of the most troublesome factors retarding the development of excellent photoresist films for ArF.